DNA-binding proteins in yeast will be investigated with specific emphasis on putative regulatory proteins which may play a role in mitochondrial biogenesis. Analyses will be carried out to examine the spectrum of DNA-binding proteins present in yeast mitochondria and to determine their biosynthetic and genetic origin. Variant polypeptide species translated in mitochondria, which we have shown to be gene products of mitochondrial DNA, will be exploited to develop a system of "gene rescue." The idea is that structural gene sequences on petite mitochondrial DNA can be expressed in zygotes obtained with matings with wild-type tester strains. Detection of expression is accomplished by the presence of unique variant mitochondrial polypeptide species present only in zygotic mixtures. Using other mutants of mitochondrial DNA, a systematic approach will be developed to map the major polypeptide structural genes on the yeast mitochondrial genome.